I went ridding down some back roads today and truck started spinning, thought it was a little weird seeing as it’s awd, stopped and put it in 4hi and turned hard to left and front tires wouldn’t pull and back tires still spinning, so my 4wd is not locking in so I found online where it says could be vaccume pump, only problem is I can’t find vaccume pump on passenger side firewall, it’s not there. Seeing if somebody can’t point me in right direction in what’s going on

 

Read this thread:

https://www.f150online.com/forums/ar...then-some.html

Do you really have AWD? If you do, there's a 4A setting on the switch.

 

Mine looks just like this, only Awd and 4Hi option